Microwave antenna



Dec. 15, 1953 G. DE PlLLOT DE COLIGNY 2,663,016

MICROWAVE ANTENNA FIG.

lNVENTOR GUERRIC DE PILLOT. DE COLIGNY,

ATTORNEYS Dec. 15, 1953 G. DE PILLOT DE COLIGNY 2,653,016

MICROWAVE ANTENNA Filed Dec. 28, 1949 4 Sheets-Sheet 2 INVENTOR GUERRIC DE PILLOT DE COLIGNY,

BY/pmk, M m (150M +1 ATTORN EYS Dec. 15, 1953 G. DE PlLLOT DE COLIGNY 2,663,016

MICROWAVE ANTENNA 4 Sheets-Sheet 3 Filed Dec. 28, 1949 INVENTOR GUERRIC DE PILLOT 01-: comm,

ATTORNEYS Dec. 15, 1953 6. DE PlLLOT DE COLIGNY 2,663,016

MICROWAVE ANTENNA Filed Dec. 28, 1949 4 Sheets-Sheet 4 INVENTOR GUERRIC DE PILLOT DE. COLIGNY 'BY/ w M, MXWM ATTORNEYS Patented Dec. 15, 1953 MICROWAVE ANTENNA Guerric dc Pillot de Coligny, Versailles, France Application December 28, 1949, Serial No. 135,482

Claims priority, application France December 29, 1948 5 Claims. 1

This invention relates to transmitting systems for projecting a plurality of divergent radio beams and more particularly for projecting divergent radio beams by means of a plurality of radiators used conjointly with a single reflector.

In the prior art, divergent radio beam transmitters using reflectors have been proposed, wherein each radiating source is placed at the focal point of a particular reflector. In other transmitters having two radio beams, two radiating sources cooperating then with a single reflector are defocalized and symmetrically situated with respect to the focus of one reflector. From such defocalized position results, a broadening out of the beam angles and of the minor lobes percentage.

One of the objects of the invention is to provide a new arrangement which permits the transmission, by means of a plurality of non-directional radiators which cooperating with a single reflector, of a plurality of differentiated divergent radio beams of substantially the same pattern.

Another object of the invention is to provide a new arrangement permitting the transmission, by means of a plurality of non-directional radiators cooperating with a single reflector, of a plurality of homothetic beams all having the same angle but having different radiation pattern ranges which are proportional to certain readily controlled and predetermined factors as set forth hereinafter.

Still another object of the invention is to provide a new cosecant squared antenna.

It is known that antennae employing a sta tionary grating type of reflector have been developed, an essential feature of which is that they utilize a focal line, i. e. a locus of points having the particular property that, for certain regions of said focal line and with an approximation neglecting the values of second order, the sharpness of focusing produced by the reflector is not affected, whatever the exact location of the radiating source along the focal line may be. Anten nae of this type, employing a stationary reflector and a non-directional radiator arranged for motion along the focal line of the reflector, have been disclosed in my copending patent application filed on the 2nd of December 1949 for Method and Device for Focusing of Radiations by Means of Stationary Reflector and Refractor Gratings, Ser. No. 130,814, now Patent No.

The object of the copending case deals with devices comprising a primary radiation source movable along the focal line, thus enabling small angular displacements of a narrow beam without affecting its sharpness.

The present invention relates to means for differentiating electromagnetic beams according to their angular elevation, which are fixed with respect to a stationary grating antenna.

To clarify the relationship between the instant application and the copending application, hereinabove referred to, it is noted that the reflectors utilized in the instant invention are the same as set forth in the copending application wherein they are termed stationary grating antennae, and which are constituted by a plurality of narrow strips of conducting material each generally disposed along a curve traced upon a given paraboloid of a family of paraboloids, said curves being defined with reference to a small movement undergone by the aforesaid paraboloids and being called in kinematics stationary characteristic line. Moreover it is understood that the antennae of the type set forth above may be rotative antennae.

According to an essential feature of the present invention, a stationary grating reflector is associated with a number of electromagnetic sources which may differ from each other by some particular feature other than the carrier frequency, these sources being fixed with respect to the stationary grating reflector and being, moreover, located along its focal line.

Different features may be used for differentiation of said sources from each other, such as dissimilar modulation frequencies or different Morse-code signals in the case of continuous waves, and dissimilar pulse frequency or time interval between main pulses and repeated pulses in the case of pulsating waves.

Under these conditions, the total beam radiated by the antenna comprises a number of pencil beams, each being associated with a given primary source and differing from the other pencil beams by the particular characteristic feature differentiating its source from the sources giving rise to the other pencil beams.

According to a second feature of the invention, pencil beams having the same angle but different pattern ranges may be obtained in accordance with the characteristics of the power feed of the primary sources, and the juxtaposition of said pencil beams gives a total pattern of any arbitrary shape.

The invention will be described hereinafter in detail with reference to several examples of its application, it being understood that these examples are not to be considered as restrictive.

3 The description will be made with reference to the accompanying drawings in which:

Fig. 1 is a plot of the trace in a meridian plane of a few members of a family of paraboloids of revolution having a common focus and axis of revolution, but drawn to different scales. Fi 1 indicates the location on each of those paraboloids of the characteristic line associated with small oscillatory motions of the paraboloids in the plane of the figure about a center of motion located at a short distance from the axis of revolution of the paraboloids. The strip refiecting elements, of an antenna according to the invention, conforming to such paraboloids, are shown fragmentarily in Fig. 1 at the positions of the characteristic lines on those paraboloids.

Fig. 2 is a perspective view of an antenna according to the invention. m

Fig. 3 is a diagram illustrating the antenna of Fig. 2 in relation to the beam patterns laid down thereby.

Fig. 4 is a diagram similar to that of Fig. 3 illustrating the provision of additional beams of the same pattern by the addition offurther radiators on the focal line of the grating reflector.

Figs. 5 and 6 are diagrams illustrating particular forms of construction for the plural primary radiation sources. 7 4

Fig. 7 is a diagram similar to that of Fig. 3, but illustrating a cosecant squared antenna pattern resulting from a plurality of beams, all of which have the same angular pattern but which are of different power; and

Fig. 8 illustrates a form of feed suitable for use in the antenna ofFig. '7.

Further, to facilitate the understanding of the present invention, the structure of the stationary grating antenna described in my above identified copending application is set forth herein, having reference particularly to Fig. 1 which is reproduced from Fig. 1 of my copending application Serial No. 130,814.

In Figure 1, I, 2, 3, 4, 5 and 6 are the traces in a meridian plane (the plane of the figure) of a plurality of paraboloids of revolution having a common focus 1,. a common axis 8 lying in the meridian plane of the figure and vertexes 9, I0, II, I2, I3, I4 the successive distances between which are equal to wherein K is an integer and A is the wavelength chosen for the primary radiator. The primary radiator is diagrammatically shown at I5, and may be considered to possess an oscillatory arcuate motion of small amplitude with respect to the parab oloids, this motion carrying the radiator through the common focus 'I and having a center of motion in the. plane of Fig. 1 on an axis I'I perpendicular to the plane of Fig. 1. The are I6 along which the radiator I5. moves therefore defines a plane containing the axis 8 of the paraboloids, and this plane is therefore meridian plane of the paraboloids. 'The'positions l8 and I9 represent the extreme positions taken by the radiator I5 in this movement.

1f the radiator is considered to. be stationary and if the paraboloids are considered instead to have an oscillatory circular motion in. the plane of the figure about H as a center, each of the paraboloids will develop an envelope for its v'arious positions assumed during this motion, and each paraboloid will interest its envelope along a line which is the stationary characteristic line of that paraboloid for that motion. As is set forth in my said copending application, the position of the portion of each moving paraboloidal surface in the vicinity of its characteristic line is stationary, within an approximation neglecting terms of the second order, and the stationary characteristic line of each paraboloid may be determined by dropping perpendiculars from the axis I? to the surface of the paraboloid in question.

The different stationary characteristic lines are the curves which are traced upon the paraboloids and which are formed by the intersections of these latter with the equilateral hyperbolic cylinders generated parallel to the axis I1 and which cut the plane of Figure 1 along the equilateral hyperbolae 2|, 22, 23, 24, 25 and 26.

All of these equilateral hyperbolae pass through the point I7, and are asymptotic to the focal axis 8. In the plane of Figure 1, the respective points of intersection 4!, 4|, 42, 42, 43, 44, 45 and 46 of the meridian parabolae I, 2, 3, 4, 5 and 6 and the hyperbolae 2|, 22, 23, 24, 25 and 26 are distributed along the strophoid 20 which has a double point at I1 and passes through focus I and then approaches line 2'! asymptotically by passing through point I'I, line 21 being symmetric (parallel) to the focal axis 8 with respect to point IT.

The stationary grating antenna comprisesa plurality of narrow metal strips disposed one on each paraboloid and conforming to a portion of the surface thereof along the stationary characteristic line of such paraboloid. All of the strips are supported on a framework and are enclosed between two. parallel planes on opposite sides of the Fig. 1 plane, equidistant from the plane of Figure 1 and parallel to the plane of Figure l', to form thereby the lateral limits of the antenna. The stationary characteristic lines 2 I26 cut the lateral planes above mentioned, both above and below the plane of Figure 1, at the points which are aligned along the curves 30, 30'.

The metallic strips comprising the antenna are represented in Figure 1 at 3|, 3|, 32, 33, 34, 35 and 36. Each strip is restricted to a narrow width on either side of the characteristic line along which it lies, i. e. to a narrow width in the dimension of the meridian plane of Fig. 1. This width may be of the order of 10 to' 20 millimeters, for example in the case of an antenna intended to operate on a wave length of 10 to 15 centimeters. In practice, to obtain suflicient reflection for the energy involved with the very high frequency emitted by radiator l5, a large number of reflecting strips are employed, for example at least or more.

The stationary grating antenna described herein, has the property that the emitted beams from radiator I5 has a pattern angle and a pattern range after reflection from the strips, whichis independent of the position of the radiator along the portion I8|9 of circle IS in Figure 1. This portion of circle I6 is the focal line of the antenna. When the radiator I5 is in the extreme position I8; the emitted beam: is: directed in a direction parallel to line 28; when the radiator is in the extreme position I9, the emitted beamis directed in a direction parallel to line 29} and finally when the radiator is at the focusfll, the emitted beam is parallel to the focal axis 8.

In the particular case where axis |'I meet's'focal axis 8, the stationary characteristic lines, instead of projecting'on the planeof Figure 1 along equi alon the focal line I6.

. p l V lateral hyperbolae, project along straight lines perpendicular to the focal axis and these stationary characteristic lines form the cross sections of the paraboloids obtained by cutting these latter with planes perpendicular to the focal axis. The line of points 4 I-46 degenerates into a circle having as its center the common focus and which passes through point I? which is then on the focal axis 8.

In Figure 2, there is shown in perspective an antenna according to the present invention. In Fig. 2, 41 designates a framework of non-conducting material, for example wood, which supports, by means of the cross pieces 48 the mounting members for the metal strips, which mounting members 99, 50, 51 and 52, 53, 54 are likewise made of wood. Central mountings 59 and 53 are formed in the profile of strophoid 20, in the re- The lateral mounting members 49 and 5I have the profile of curve 39 and the lateral mounting members 52 and 54 have the profile of curve 39.

These various mountings hold the metallic strips of the reflector 3I36. In the antenna of Fig. 2,

a plurality of microwave radiators 31, 38 and 39 adapted to radiate energy of the same carrier frequency, are supported from the framework 61 by means of a structure 49 to lie at spaced points The radiators may be positioned equiangularly along the circular arc IS, in which case the lobes or beam to which they give rise will be equiangularly inclined. The radiators 37-39 may be fed from a common source of microwave energy such as a magnetron 40'.

Referring to Figure 3, a radio beacon, having a wave length of centimeters for example, comprises a framework 55 supporting a plurality of metal strips 56 which are disposed in accordance with the explanation hereinabove given in connection wih Fig. 1 to provide a reflector and a series of microwave radiators 58, 59, 69 disposed along the circular focal line 57 of the array of reflecting strips 56, this focal line corresponding to the focal line I6 of Fig. 1.

These radiators are schematically illustrated in Figure 3, and are further shown in greater detail in Figure 5. 'Framework55 may be rotated about the shaft 35 which is fixed on base 62.

The reflector is schematically shown at B3 in Figure 4. 64 denotes the plane of symmetry of the antenna which contains focal lne 51 and radiators 58, 59 and 99. Radiator 58 provides beam 68, radiator 59 beam 69, radiator 69 beam I9 etc. The spacing of the radiators along the focal line isso disposed as to have a certain'predetermined angular spacing between the two axes of successive beams. This angular spacing between two successive beams is equal to the angular spacing between the two successive radiators along the circular focal line, as viewed from the center of the circle.

The radiators are represented on Fig. 5, as open end rectangular wave guide radiators 58, 59, 69 which are aligned along the circular focal line 51. Wave guides 65, 66 and 61 are provided with T-R boxes I5, I9, 'I'I operated by their keep alive electrodes I8, I9, 89.

The keep alive electrodes may be operated in such a manner that the nth radiator, starting from the one, 58, giving the pencil beam 68 closest to the horizontal position is fed one pulse out of n For example,

pulses produced by magnetron I2.

6 radiator 58 radiates all the pulses, radiator 59 one pulse out of two, radiator 69 one pulse out of three and so on.

Under these conditions an aircraft located at M (Fig. 4) can not only determine the bearing of the radio beacon, by comparing the instant when the radio beam of plane 99 are received in the aircraft with the instant when the same plane passes through the north direction 8I and which instant will be indicated in some conventional manner, but the aircraft can also determine'its angular elevation by measuring the frequency of recurrence of the pulses received. With this information the aircraft bearing and angular elevation are known and if the altitude is, moreover, supplied by some other device, the aircrafts exact geographical location is known.

A high degree of accuracy cannot be obtained from this device at a great distance from the radio beacon; but nevertheless it has a desirable use, for instance, in case of approach to an airfield having intensive trafiic, or other conditions, since such a radio beacon enables the aircraft to determine its position while maintaining radio silence.

Fig. 6 represents another method for differentiation of the radiators located along the focal line 51. Each individual guide 65, 59, 91 the open ends of which constitute the radiators 59, 59, 60 is by-passed by a second individual wave guide 85, 86, 81 comprising respectively delay lines 82, 83, 84. Thus for each source, every pulse transmitted by the main guide ll is radiated by all radiators and is repeated by each radiator with a specific delay, for instance a delay of 11. microseconds for the nth radiator. 88--89, 999I, 92-93 are T-R boxes the duplexers 88, 99, 92 being controlled through their keep alive electrodes by power taken off respectively from guides 85, 86, 81 and the duplexers 89, 9|, 93 being controlled in their turn by power taken off respectively from guides 65, 66, 61.

This embodiment, although it complicates the differentiation, may be preferable on account of its greater accuracy in determination of the angular elevation, its greater range, and a more convenient operation of the magnetron (this embodiment requires a lesser frequency of recurrence than in the first case) Figures 7 and 8 refer to antennae having any desired predetermined outline of polar graph of their amplitudes. panoramic search radar antennae it is desirable to obtain such a graph, in the vertical search plane, that the echoes of objects situated at any distance, but located at a similar altitude, be comparable. It is thus desirable to have an antenna of a so-called cosec type, i. e. for a direction situated in the vertical plane and making an angle A with the horizontal line, it is desirable to obtain a power density pattern proportional to cosec A, or a field intensity pattern proportional to cosec )t.

The reflector is schematically illustrated at 94 in Figure 7. 95 indicates the plane of symmetry of the antenna and contains focal line 9! and radiators 98, 99 and I90. Radiator 98 provides beam I98 which makes an angle M with the horizontal, and which has an intensity proportional to cosecant M. Radiator 99 provides beam I99 which makes an angle M with the horizontal and which has an intensity proportional to cosecant M. Radiator I99 provides beam I I0 making an angle A2 and having an intensity proportional to cosecant Az.

It is known that for certain Radiators 98, 99 and I0!) are ali ned along the focal line 91 of the reflector 94, shown in Figure 8. As set forth in the foregoing description, the radiators 98, 9,9 and H19 are oonstituted by the open ends of rectangular Wave guides IOI, I02 and I83. Each of thesewave guides is provided with a diaphragm H34, H15, lfifi controls ling the power supplied to the radiators direct ratio with cosec A. In this arrangement the penci1 beam associated with each radiator will have an intensity proportional to cosec and since the total beam is formed by the adjacent component pencil beams, the total beam will have for each direction making an angle A with the horizontal direction an intensity proportional to .cosec A, It is also possible to give to the polar graph of the whole pattern any desired predetermined out line.

It is understood that numerous variations in the preceding arrangement may readily be effected Without departing from the description, spirit and intent of the foregoing invention, and that further it is not necessary to have the radiators separated by gaps since, if desired the single radiator can be constituted by a slot out along cylindrical or tapering Wave guides.

What I claim is:

1. An antenna adapted to lay down a plurality of radio frequency energy beams of similar directivity properties and having coplanar axes angularly inclined to each other, said antenna comprising a plurality of radiators capable of emitting radiation of the same carrier frequency,

said radiators being located at spaced points along frequency, said surfaces having in a common 1 meridian plane of said paraboloids a small extension on either side of the intersections with said paraboloids respectively of the perpendiculars to said paraboloids drawn from the center of said circle.

2. An antenna adapted -to lay down a plurality .of .angularly inclined radio frequency energy beams of substantially the same directiv-ity proplerties, said antenna comprising a plurality of radiators adapted to radiate energy of the :same

carrier frequency, means to support said radiatorsat spaced locations along the arc.,of a circle, a plurality of metallic reflector elements each having a surface conforming substantiallyto :a portion of a paraboloid of revolution, the paraboloids to which said surfaces conform being membersof afamily of paraboloids having acornmoh focus on said circle a d a axi o re o ut on in n. th l ne of toidoiro e. tho ort s o aid a ebo oid being s ed rom ac the by int g a mu i l s o e hal the v en h co espond g to a f e ency. sa d surfac s havin i the common er d pla e o sa d ra oloid cont i g t e a e of said circle a small extension on either side of the intersections with said paraboloids respectively of the por en io lars o a d pa a o o s w oft i aidmorid ah plane fr m he cent r o said circle.

3, an enna da ted o y own a l rality o rad f uenc energ eam of subs ntia ly he som s it otivi y p op ie a d a ing oolo he axe id en co p n a plural t of radiators dimensioned to radiate electromagnetic energy of the same carrier frequency, a plurality of metallic reflector elements each havn a surfac on orm g su ta all o a porion f arabo o d of e o the par b loids to which said surfaces conform being meme s o a fam l o pa abo isis h n a c mmon.

focus and axis of revolution, the vertices .of said paraboloids being spaced from each other sub.- stantially by integral multiples of one-half the w ve n t cor po in t s i requen y. mo n supp ng s d lement wit their urfaces substantially lyingin the surfaces of their es ec e pa b i s. and means su p t n sai radiators at spaced locations along an arc of a circle intersecting said common focuathe plane of said circle containing said common axis .of revolution, the surfaces of said elements having in said plane a small extension on either side of the i rs t on wit said p re ol ds r ectiv ly of the perpendiculars to said paraboloids drawn in said plane from the center of said circle.

4. An antenna according to claim 2including a source of radio frequency energy and a plurality of transmission lines coupling said source to said radiators, said transmission lines including attenuation elements, whereby the intensity of said beam varies from beam to beam.

5. An antenna according to claim 3 including a source of pulsed energy, transmission lines coupling said source to, said radiators, and means short-circuiting said transmission lines at varying rates.

GUE RIC ,DE LL DE L GNY- References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,039,812 Leib et a1. May 5, 1936 2,217,321. Runge et al Oct. 8, 1,940 2,367,764 Ferris Jan. 23, 1945 2,408,435 Mason Oct. 1, 1946 2,426,992 Folland .et'al Sept. 9, 1947 2,435,988 Varian Feb. 17, 1948 2,530,580 Lindenblad Nov. 21, 1950 

